The news that malaria kills almost twice as many people a year as previously believed — not 655,000 but a staggering 1.2 million — is only the latest evidence of how poorly even the best scientists and researchers understand the poor world. The error derived from the mistaken assumption that malaria is a child killer, says a report in the Lancet by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington. The institute found that if deaths in children over 5 and adults were studied more closely, then more than 78,000 children ages 5 to 14, and more than 445,000 people ages 15 and older, were found to have died from malaria in 2010, meaning that 42% of all malaria deaths were accounted for by people ages 5 and older.

If correct, at a stroke that overturns medical consensus, makes nonsense of decades of World Health Organization (WHO) statistics — the official malaria numbers — and plunges the current multibillion-dollar antimalaria campaign, and the push to reach a 2015 deadline for achieving the eight Millennium Development Goals, into grave doubt. “You learn in medical school that people exposed to malaria as children develop immunity and rarely die from malaria as adults,” said Dr. Christopher Murray, IHME director. “What we have found in hospital records, death records, surveys and other sources shows that just is not the case.”

For its part, the WHO disputed the new figures, saying IHME had used unreliable verbal testimony, rather than clinical autopsies, to arrive at its figure. “We stand by our estimates,” said spokesman Gregory Hartl.

Full disclosure: I wrote a book last year, Lifeblood, about the global campaign against malaria. In it, I hailed the campaign’s remarkable success in reducing deaths from one of the world’s deadliest diseases. And I argued that its central insight — that fixing disease was as much an economic concern as a humanitarian one — and its innovations, which mostly centered on adapting business techniques to foreign assistance, heralded a whole new way for both business and aid, and at a time when both were in danger of losing their way. The statistical backbone of the book was the WHO’s numbers.

The IHME does not dispute that the malaria campaign is having a profound effect. According to its numbers, deaths have declined dramatically since 2004, when they reached 1.8 million. So, this is still a very effective campaign, and one for all aid workers to study.

But the IHME claims that if the WHO did measure the trend correctly, it woefully underestimated the size of the problem. The IHME uses its figures to argue that that means even more resources should be poured into the malaria fight. That seems premature before the WHO and the IHME have even figured out who is right. And the bigger point is this: this is not the first time the people running developing-world health campaigns have been shown to have only the loosest understanding of the problems they are tackling. The IHME’s report was followed a day later by one from the Indian Council of Medical Research that claimed malaria deaths in India were 40 times as high as previously estimated. I was a reporter in India in 2005 when — to humiliated outrage from the Indian government — that country briefly but officially became home to the world’s largest HIV/AIDS epidemic with more than 5 million infected. Two years later, new research halved the total number of those affected. Likewise in South Africa, I followed reports in 2009 that predicted the number of HIV/AIDS orphans would be 5 million by 2015, a catastrophic figure for a nation of 50 million whose townships are already raging with delinquency. This year, that figure was quietly cut by three-quarters.

Some people look at these statistical about-faces and smell a rat. They conclude that aid workers and health campaigners manipulate figures for their own purposes: to give the impression of a crisis in a fundraising drive or make out that a catastrophe has been averted when it comes to performance assessments. As any developing-world reporter can tell you, that certainly does happen. But the disputed malaria figures would seem to reveal a different truth. In a world that sometimes seems wondrously connected, and where people worry about information overload, it’s a sobering thought that, more often than we’d like, we really don’t know what’s going on out there.